The Republicans have passed their tax bill, without a single Democratic vote, despite low to dismal poll ratings. It's reminiscent of the passage by Democrats, without a single Republican vote, of Obamacare in March 2010.

Democrats lost 63 seats and their House majority that fall. Republicans hope they won't follow suit. They argue, accurately, that their bill will lower taxes for almost all taxpayers and that it will stimulate economic growth, which already has risen above the growth in the Obama years.

The effects of Obamacare, in contrast, were harder to model, and some backers' claims -- if you like your insurance, you can keep it -- soon were revealed as glaringly untrue. We'll see whether the greater simplicity of the tax bill makes a difference in political fallout.

One thing in common between the two bills is that voters have seemed congenitally skeptical about the claims of the party in power. Obamacare continued to be unpopular until, presto, Donald Trump took office and Republicans threatened repeal.

A second thing in common is that the details of both signature pieces of legislation -- details that weakened their appeal and provided ammunition for opponents -- were the result of legislative straitjackets created in the 1970s.

The restrictions of the Congressional Budget and Impoundment Control Act of 1974 and the cost estimates of the Congressional Budget Office it created were intended to provide clarity and restraints on presidents and Congresses. Ironically, we had mostly balanced budgets before 1974 and have had mostly budget deficits since.

Another 1970s reform that has proved counterproductive involved changes in Senate filibuster rules. The number of votes needed to end a filibuster was reduced from 67 to 60, and filibusterers were no longer required to hold the floor, speaking all night if need be, to block passage of legislation. The result: many more filibusters than before and an effective requirement -- unimagined when I was writing the first edition of The Almanac of American Politics in 1970 -- of a supermajority of 60 votes to pass major bills.

As any student of political behavior might have predicted, both parties have learned to game these systems. Obamacare and the tax bill provide many examples.

Democrats got the Congressional Budget Office to count the revenue generated by Obamacare's Community Living Assistance Services and Supports, or CLASS, Act taxes, fully realizing that program's postponed and unsustainable costs would never be incurred. Republicans likewise took some $300 billion of savings, suddenly available when the CBO revised its clearly mistaken estimates of costs of repealing Obamacare's individual mandate, to pay for tax cuts they couldn't otherwise get.

This is not a criticism of the CBO, which has remained properly nonpartisan and which was designed to estimate revenue flows, not personal choices -- such as how many young people would rather pay small individual mandate penalties rather than expensive Obamacare health insurance premiums.

It's a criticism of the notion that you can create neutral rules that will guide elected politicians to desired results. Politicians and the voters they represent have policy goals they believe important, and they have their own ways -- fallible but subject to criticism and debate -- to estimate the likely effects of particular policies.

My observation over the years is that systems intended to be fail-safe are sure to fail. Forty-three years of the Congressional Budget and Impoundment Control Act regime and 32 years of the opaque Byrd rule, which allows some Senate measures to pass with 50 votes whereas others require 60, have shown that both parties have figured out how to game the rules enough to foil their intended purposes.

The Constitution provides rules enough by allowing one Congress to repeal the laws made by a predecessor (rendering Obamacare's yet unimplemented Independent Payment Advisory Board unconstitutional) and by allowing each house to set its own rules. The Senate has enough other dilatory procedures to fit Thomas Jefferson's description as the saucer in which coffee can cool, and any House majority is subject to recall in 22 months.

Economic conditions often veer from the CBO's predicted flight paths, and foreign developments or domestic attacks can change national priorities. Congress should be free to respond.

The Republican tax bill is vulnerable to attack because it will cut the corporate tax rate from 35 percent, highest among developed countries, to 21 percent -- even though economists of every stripe and Barack Obama said it should be lowered.

Surprisingly, Republicans in the Trump era took the responsible step of cutting the rate, at some political risk. Any chance they'll clear away the detritus of the long-dysfunctional 1970s reforms and relegate them to the fate of bell-bottoms and disco?